Volume control



Nov. 29, 1932. w, E, G.LB'ERT 1,889,018

VOLUME CONTROL Filed July 29. 1951 2 Sheets-Sheet 1 llll ' I menial Nov. 29, 1932. w. E. GILBERT VOLUME CONTROL 2 sheets sheet 2 Filed July 29. 19:51

Patented Nov. 29, 1932 UNITED STATES PATENT OFFICE WALTER. E. GILBERT, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR T0 ATWA'IER KENT MANUFACTURING COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CQRPO- BATION OF PENNSYLVANIA vomms conrnor.

Application filed m 29, 1931. sen-. 1 No. 553,723.

My invention relates to methods of and apparatus for controlling the volume of reproduction of signals received by radio receiving systems.

Heretofore, systems for automatically compensating for fading of received signals, and

for the great difierence between weak, dis-' tantsignals, and strong, local signals required one or more additional tubes and complicated circuits.

In accordance with my invention, the sensitivity of receiving apparatus is automatically and inversely varied with the amplitude,

or variation in amplitude, of incoming sig-' nal energy without need for additional tubes and without substantial modification of the receiver, to maintain a desired volume of reproduction.

More specifically, tlve biasing voltage applied to the grid of one or more radio frequency amplifying tubes is comprised oftwo components; one of which is substantially constant in magnitude, and the other of which varies in magnitude with the signal and is an opposing voltage derived from the anode current of a detector tube; more specifically and preferably, the maximum magnitude of the second or variable component is less than that of the fixed component.

Further in accordance with my invention a suitable source of negativegrid biasing potential and a conductive impedance, specifically a resistance, are connected between the cathode structure of one or more radio-frequency amplifier tubes and the detector anode, with the grids of said amplifier tubes connected to a suitable point in the impedance.

In pne modification of my invention, thenegative, fixed component of the grid bias is derived from the flow of anode current of the receiver through the field winding of a dynamic speaker, and the'positive,'var iable component is derived from high resistance connected between the negative terminal oi the field winding and the detector anode;

more particularly, the field windingis included in a filter system. for the anode current of the receiver, and to prevent the variable component of the grid bias voltage from changing at the frequency'df the anode cur- Fig. 1 is a schemmatic diagram of a simple receiving system utilizing the invention.

superheterodyne receiver operating from an alternating current source and utilizing my invention.

Referring to Fig. l, the input circuit of the Fig. 2 is a detail wiring diagram of a radio frequency amplifyingtub'e 1 is coupled, 1

as by the transformer 2, to. the antenna system 3. The input system of the. tube comprising the secondary of the transformer 2 is preferably tuned as by condenser {l to the frequency of the received signal. The input circuit of the detector tube 5, comprising the inductance 6 and tuning condenser 7, may be coupled to the anode circuit of the amplifier tube 1, or there may be interposed one or more additional stages of radio frequency amplification. The battery 8 suitably biases the control grid g of the detector tube 5 so that it operates as an anode circuit rectifier, the average plate current increasing for increased amplitude of received signal and vice versa. For simplicity, the anode circuit are of the screen grid type, the resistance 12 interposed between the positive terminal of the battery and the anode detector 5;, is an audio frequencyimpedance into which the 86 of the detector is shown as supplying tele-j phones 9, through a blocking condenser 10',

detector 5 operates. The same battery may be utilized for supplying the shield grids of the tubes, the resistances 13 and 14 suitably reducing the potential.

vbattery 21, is of'substantially constant mag-' e circuit thus far described is a conventional circuit of which it is characteristic that the volume of signal heard in the telephones 9 varies with the signal amplitude, so that if due to transmission attenuation or other conditions, the carrier amplitude varies, the reproduced signal in the telephones correspondmgly varies; further, the response in the phones is great for strong incoming signals and small for weak incoming signals. In accordance with my invention the volume of the reproduction remainssubstantially the same for a wide range in the variation of the amplitude of the radio frequency carrier, and without addition of tubes or substantial modification of the circuit.

As above stated, the average value of the detector anode current varies with amplitude of the impressed signal, increasing for increased signal and vice versa. The potential of point 15 in the anode circuit of the detector 5 with respect to ground 16, or equivalent, varies substantially, for example,

100 volts, fromno signal to maximum signal.

This variation of potential is utilized automatically to vary the bias applied to the grid of the radio frequency amplifier tube 1 to modify automatically the sensitivity of the radio frequency amplifier system, so that for strong signals the sensitivity is decreased. Specifically,betWeen the point 15 and round 16, to which the cathode c of the ra io frequency amplifier tube is connected, are connected the resistances 17 18 and the battery 21, the control grid of tube 1 bein connected as by conductor 19 to a oint 20 etween the resistances. A single resistor suitably ta ped to provide point 20 may of course be su sti-- tuted for resistances '17, 18. The resistance 18 whose positive terminal is connected to the point 20 and whose negative terminal is connected to ground 16 through the battery 21, serves as a meanstending to make the con trol grid of tube 1 positive with respect to its cathode c, the potential diiiierence between the electrodes varying with or proportionally to the potential of point 15 in the anode circuit of the detector, which as previously described is dependent upon the carrier amplitude of the received signal.

Between the points 20 and 16, and specifically between the, negative terminal of resistance 18 and ground,'is connected a suitable source of negative grid biasing potential,'for example, a battery 21 whose negative terminal is connected to the control grid 95' of the radio frequencyamplifier tube.

The biasing voltage impressed upon the grid of the tube 1 therefore, has two opposing components, one of which, produced by the nitude and the other of which producedby i the resistance 18, varies in magnitude with the amplitude of the received radio frequency carrier. The voltage of the battery aeeaora is 15 volts, leaving a resultant of three volts for negatively biasing the grid of the tube 1, which may be of the R. G. A. 232 type.

When the signal is impressed upon the detector, the relative magnitudes of the biasing components change. For example, under conditions of maximum signal the voltage drop across resistances 18 and 19 may decrease about 100 volts, so that for the values of resistance given the drop across resistance 18 decreases 9 or 10 volts, and the resultant negative bias potential for the control grid of tube 1 therefore increases from three volts negative to 12 or 13 volts negative. This increase in the negative bias decreases the sensitivity,oramphfying abilit of the radio frequency stage, or stages, and once reduces the volume of signal reproduced by the telephones 9, or equivalent. For signal amplitudes of intermediate value, the grid bias changes substantially proportionally, so that signals widely differing in amplitude are reproduced at substantially the same volume by the telephones.

Between the point 20 and ground 16 is connected a by-pass condenser 22 of such value that the time constantof the combination of resistance 17 and condenser 22, is low, and corresponds to-a frequenc lower than the lowest signal frequency which is reproduced; for example, when the resistance 17 is of the above value of about two megohms, the condenser 22 may have a capacity of about .1 microfara-d, the combination having a time constant of .2 seconds, which is equivalent to five cycles.

In the superheterodyne receiver of Fig. 2, the first detector 23 is preceded by a presclector system generally Indicated at 24. The frequency to which the oscillator 25 is tuned, suitably differs from the frequency to which the preselector system 2 1 is tuned, so that the signal energy, in the usual manner is amplified at an intermediate frequency by the frequency amplifier 26, which supplies the second detector-27 of the system. Theoutput system of the detector is coupled to a suitable audio frequency amplifier system, for example to the input circuit of the pen tode vacuum tube 28, (R. C. A. 247 type) having'in its output circuit a transformer 29 whose secondary supplies the voice coil 30 of a dynamic loud speaker 40. I

The field coil 21' of the loud speaker is included in the negative conductor of the anode currentsupply'section of the power supply system 31, and the drop of potential across the field coil is used for negative grid biasing purposes, as well as serving asv a filter choke.

For the purpose of illustration it is assumed that the output voltage of the supply system 31 is 220 volts, and that the resistances 33 and 34 in series in the positive conductor to the detector anode are respectively ap-- proximately 250,000 and 65,000 ohms. With no signal present, and using a type 2% tube, the voltage drop across the resistances 33 and 34 is approximately volts, so that the point 15' is approximately 160 volts posi-' spectively by the loud, speaker winding 21,

and the resistance 18' are in OPPOSltIOH so that the resultant grid biasing voltage under conditions of no signal is three volts negative. In the system specifically illustrated, this biasing potential is applied to the grid of the first detector and an intermediate radio freing signal, thepotential of thepoint 15' with respect to earth, will drop to a proximately volts. For the values 0 resistances 17 and 18, given above, the voltage across 18 will vary from 117 volts with no signal, to about 87 volts for maximum signal. Since this variation is opposed to the constant 120 volt drop across the speaker field 21' the bias. upon the grids of the control tubes automatically varies from a m'nimum of 3 volts negative to about 33 volts negative with the range of no signal to maximum signal. Briefly expressed, the negative bias is automatically controlled so that the sensitivity of the receiving set is substantially inversely proportional to the strength of the incoming signals.

While specific values of resistance, voltages and types of tubes have been given for clarity of explanation, it will be understood that other values of resisiances,'and types of tubes,

may be used.

The condenser 22 is of such value that the combination of the resistance 17 and condenser 22 have a time constant corresponding to a frequency lower than the lowest reproduced frequency. For the value of the resistance 17 above given, the condenser 22 may have the value of about .1 microfarad.

In the system of Fig. 2, since the resistance 18' is connected to an intermediate point of the filter system, there is possibility of the biasing potential fluctuating at the frequency of the alternating current source 35 which is connected to the power supply source 31.

To prevent this undesired fluctuation, a condenser 36 of suitable value is connected between the earth and a suitable point 37 of resistance 18. The resistance from point 37 to point 20' may be approximately 1.8 megohms and from point 37 to the more negative terminal of the speaker field winding 21', about 500,000 ohms. For these values of resistances, the condenser 36 may have a capacity of the order of .1 microfarad.

It is usually desirable to provide means for manually selecting the level at which the signals are to be reproduced; for example, contact 38 is adjustable along the potentiometer resistance 39 to determine the proportional amount of the total signal voltage that is applied to the grid of the pentode tube. In operation, the user of the apparatus moves contact 38 until the volume of the received signal attains the proper value, and the automatic grid biasing. arrangement above described, thepeafter varies the sensitivity of the amplifier for variations in signal strength to maintain the selected volume of reproduction, substantially independently of fading,

and substantially irrespective of the power or distance of the transmitting station. It will be understood that other types of manual volume control may be used, and in diflerent parts of the circuit, for selection of the desired volume level.

What I claim is:

1. In a radio-receiving system comprising a radio-frequency amplifier tube and a detector tube, a source of anode current, a conductive impedance connected between a positive terminal of said source and the anode of said detector tube,-means for automatically varying the sensitivity of the system comprising conductive impedance connected between the anode of said deteptor tube and the cathode of said amplifier tube, a connection from the grid of said amplifier tube and an intermediate pointof said impedance, and a source ofnegative grid-biasing potential included in series with said impedance between said cathode and said point.

2. A radio receiving system comprising a radio-frequency amplifier tube, a detector tube, a source of anode current for said tubes,

a conductive impedance connected between the positive terminal of said source and the anode of said detector tube resistance means between the negative terminal of said source and the cathodes of said tubes, resistance means between the anode of said detector radio-frequency amplifier tube, a detector tube, a source of anode current for said tubes, a conductive impedance connected between a positive terminal of said source and the anode of said detector tube, resistance means be.

' tector tube, a source of rectified alternating current for supplying anode current for said tubes, an automatic sensitivity control system comprising a filter impedance between the negative terminal of said source and the cathodes of said tubes, resistance means between the anode of said detector tube and said negative terminal, a connection from the grid of said amplifier tube to an intermediate point of said resistance, and a capacity connected between the cathode of said amplifier tube and a point of said resistance between said negativeterminal and said grid connection.

5. lln a superheterodyne receiver utilizing radio frequency amplifying tubes and detector tubes, an automatic sensitivity control system comprising means for biasing the grids of said amplifying tubes comprising means for producing'a substantially constant voltage, means for directly and solely deriving from the anode circuit of the second detector tube, an opposing voltage whose magnitude varies inversely with the amplitude of received radio-frequency energy, and

means for preventing the resultant of said voltages from varying at a frequency within the range of reproduced audio-frequencies.

6., In a radio receiving system comprising radio-frequency amplifying tubes, and a' detector tube operating toell'ect anode circuit rectification, means for automatically varying the sensitivity of the system comprising means for negatively biasing the control grids of said tubes including means for producing a voltage of substantially fixedmagnitude which is greater than and opposed to a second voltage, whose magnitude is inversely proportional to the amplitude of received signal reeaoie negativel big the control grids of said tubes inc uding means for producing a volt age of substantially fixed magnitude which is greater than and opposed to a second voltage, whose magnitude is inversely proportional to the amplitude of received signal energy,.and resistance in the anode circuit of said detector, from which said second voltage is directly de-' rived, and capacitative means cooperating with said resistance to prevent variation of the potential of said grids at a frequency within the range of reproduced audio-irequencies.

i 8. In a radio receiving system comprising radio frequency am lifier tubes, a detector tube, and a source 0 anode current for said tubes, an automatic sensitivity control system comprising means for producing a negative biasing potential of substantially constant magnitude including an impedance traversed by the anode current of said tubes and connected between the negative terminal of said source and the cathodes of said tubes, means for producing an opposing biasing potential varying with signal intensity comprising resistance means connected between the detector anode and said negative terminal, and a connection from the grid of at least one of said amplifier tubes to an intermediate point of said resistance.

9. In a radio receiving system comprising radio-frequency amplifier tubes, an audio amplifier tube, a detector tube, and a source of rectified alternating current for supplying anode current for said tubes, an automatic sensitivity control system comprising means for producing a negative biasing potential of substantially constant magnitude including a filter impedance traversed by the anode current of said tubes and included between the negative terminal of said source and the cathodes of said tubes, means for producing an opposing biasing potential varying with signal intensity and whose maximum magnitude does not exceed said negative biasing potential comprising resistance means connected between the detectoranode and said negative terminal, and a connection from the grid of at least one of said amplifier tubes to an intermediate point of said resistance.

WALTER E. GILBERT.

energy, and resistance in the anode circuit of said detector from which said second voltage 7. In a radio receiving system comprising radio-frequency amplifying tubes, a detector tube operating to eflect anode circuit rectificatio n, means for automatically varying the sensitivity of the system comprising means for CERTIFICATE OF CORRECTION.

Patent N0 1,889,018. i November 29, 1932.

WALTER E. ammunit is hereby certified that enter appaars in the printd specification of the alum/e numbered patent iequiring carreciim as follows: Page 4, iine l8, ciaim 4,; strike out tine Ward "and", and insert the same aim "Rube." imline 19; and. mm fih e said-Letters Patent simuid be read with this carmction therein that the samdmay conform to the ream-d 0f the case in the Patent Office.

Signed and seaied this iiith day of January, A. 'D; 1933.

, v M. J. Moor. (Seal) Acting Commissioner of Patents. A 

